File I/O

# Write text
File.write("data.txt", "line 1\nline 2\n")

# Read entire file
puts File.read("data.txt")

# Read line by line (auto-closes)
File.foreach("data.txt") { |line| puts "[#{line.chomp}]" }

# Append
File.open("data.txt", "a") { |f| f.puts "line 3" }

# File info
puts File.exist?("data.txt")
puts File.size("data.txt")

# Path operations
puts File.basename("/a/b/c.txt")       # c.txt
puts File.dirname("/a/b/c.txt")        # /a/b
puts File.extname("c.txt")             # .txt
puts File.join("a", "b", "c.txt")

# Directory traversal
Dir.mkdir("samples") unless Dir.exist?("samples")
Dir.glob("*.txt").each { |f| puts f }

# CSV with stdlib
require "csv"
CSV.open("people.csv", "w") do |csv|
  csv << %w[name age]
  csv << ["Alice", 30]
end

CSV.foreach("people.csv", headers: true) do |row|
  puts "#{row['name']} is #{row['age']}"
end